1. Field of the Invention
The present invention relates to a module circuit which integrally combines a circuit of a meter board and switches incorporated into an instrument panel of automobiles with an internal circuit of an electric junction box.
2. Description of the Prior Art
Inside and outside the instrument panel of automobiles, there are many instrumentation components, as shown in FIG. 8, such as switches a, units b, and meter boards d with built-in meters c, leaving the installation space crowded with complex wiring. The wiring harness W around the meter board, in particular, has a large number of wires installed. The crowded condition is further compounded with many joints and branch lines w. To alleviate the situation and simplify the wiring, a joint box B is installed in addition to an electric junction box A containing fuses and relays (as disclosed by the Japanese Patent Preliminary Publication No. Heisei 2-45238).
FIG. 9 is an example wiring diagram of a lamp circuit using the above-mentioned electric junction box A and joint box B. In the figure, reference numeral 1a, 1b, 1c represent connectors provided to the box B; 2a, 2b, 2c switches; and 3a, 3b, 3c indicator lamps. Because five joint connections 4a, 4b to 4e are installed inside the box B, wires 5a, 5b to 5g, which constitute the trunk portion w0 of the wiring harness and are connected to the electric junction box A, are free from joint wires (branching wires connected to other wires).
However, the space available for the installation of the joint box B is not large enough to accommodate all joints. The circuits for switches a, units b and meters c are mostly related with the circuit of the electric junction box A, which is usually installed in a right lower part of the dashboard in front of the driver's seat. Hence, many of these circuits run back and forth between the electric junction box A and the meter board d.
In FIG. 9, connecting the box B, the meter board d and the switches 2a to 2c requires a total of nine connecting wires 6a, 6b to 6i. The box B is connected with 15 wires through the connectors 1a to 1c. Since there are device-to-device connecting wires between the box B and the meter board d, such as 6a, 6b-6e, wires are still closely entangled. In the figure, designated 7 are fuses provided in the electric junction box A, 8 a relay, and 9a-9d wires forming another trunk portion w0 of the wiring harness.
The aforementioned Japanese Patent Preliminary Publication No. Heisei 2-45238 proposes a wiring configuration which further reduces the number of required wires and thereby simplifies the wiring by providing in the internal circuit of the meter board a branch circuit having joint connections for the meter board and the wiring harness so that the meter board itself can accommodate the joints.
FIG. 10 shows an example of a lamp circuit with the branch circuit installed in the meter board d. That is, the joint connections 4a-4e of the box B in FIG. 9 are all accommodated in the meter board. The meter board d is provided with connectors 1a'-1c' instead of connectors 1a-1c, which were attached to the box B.
From comparison between FIG. 10 and FIG. 9, it is obvious that the wiring configuration of FIG. 10 obviates the box B and further eliminates the device-to-device connecting wires 6a-6e between the meter board d and the box B, significantly reducing the number of wires and also branch wires.
FIG. 11 shows an example switch circuit with the branch circuit installed in the meter board d. Since an appropriate number of joint connections 4 are installed inside the meter board d, two switch bases 10a, 10b are directly connected by straight wires 5, 5' having no branches. The meter board d and the electric junction box A are also connected by straight wires 5g-5j. Reference numerals 9e, 9f-9h are wires forming a trunk portion w0 of the wiring harness as in the case of FIG. 10.
Since the prior art of FIG. 10 and 11 have accommodated in the meter board d only the joints and joint box located near the meters, a large number of wires running between the electric junction box A located in the lower right portion of the dashboard in front of the driver's seat and the meters are left as is (such as wires 5a, 5b-5j). Therefore, the wiring harness still has a complex configuration, requiring many manufacturing hours and high cost. Connecting the terminal connectors of the wiring harness with the instrumentation components in a small space inside the instrument panel is difficult and requires many assembly steps.